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978-3-8439-1128-3, Reihe Elektrotechnik
Investigations of Off-Line and On-Line Monitoring and Diagnosis Methods on Power Transformers
222 Seiten, Dissertation Universität Hannover (2012), Softcover, A5
Power transformers are one of the most important and most expensive components in electric energy networks. The most frequent cases of failure of transformers are tap changer, active component and bushings. On-line monitoring and diagnosis of active part and bushings through enhancing its off-line methods are the subject mater of this investigation.
One part of this contribution reports on a detailed study of the effects of ageing, temperature and moisture on frequency and time domain spectroscopy measurements carried out on oil-impregnated pressboard samples as well as on a transformer under controlled laboratory conditions. Furthermore, the insulation system was monitored via its oil temperature and water content by an on-line monitoring system over a period of about 45 days.
In the second part, a new on-line monitoring and diagnosis method of power transformer bushing through its bushing tap or a non-invasive capacitive sensor (NICS) is introduced. An air-gap capacitive sensor as a normal capacitor is used to create a voltage reference due to calculating tan delta and capacitance of the bushing. Furthermore, with designing and developing the measuring system via an electrical-optical data transferring system, on-line monitoring in normal condition, short-circuit between layers, bushing oil leakage, different temperature and different environmental conditions were investigated.
Winding deformation and inter-turn fault are two winding failures. If Inter-turn fault is not quickly detected, a more serious fault will develop which would cause irreversible damage to the transformer. In this part, a new technique for on-line transfer function (TF) monitoring of power transformer through its bushing taps or NICS in the time and frequency domain on some distribution and power transformers is presented. Furthermore, it is shown that the method can detect an inter-turn fault for about 0.2% of winding.
The last part of this research introduces a multi-channels on-line monitoring system. A modular design of a monitoring system starting with the most important parameters to detect failures seems to be reasonable and can be completed depending on the individual requirements of the user. A modular on-line monitoring system for PD, tan δ and capacitance of a high-voltage bushing and winding TF seems to be an efficient system.